It depends upon whether your LLC is a single member LLC or a multi-member LLC.
If your LLC is a single member LLC, then the IRS treats it as a disregarded entity which means that a separate tax return is not required for the business entity and the business activity is to be reported on your personal tax return on Schedule C, E, or F (depending upon the type of business). If you have already filed your personal return, then you will need to file an amended return (Form 1040X) to add your business activity to it. If you have not already filed your personal income tax return, then an extension for your personal return will also cover your business. See more information here: Single Member Limited Liability Companies | Internal Revenue Service
See the steps below to file an amended return in TurboTax:
https://ttlc.intuit.com/replies/7276605
If your LLC is a multi-member LLC, then you will need to use TurboTax Business to file the extension and eventually, the tax return (Form 1065) for the entity. Below are the instructions to file an extension in TurboTax Business:
https://ttlc.intuit.com/replies/3301655
